The prior art is replete with various systems for detecting the height of a combine header above the ground surface and for automatically adjusting the header height during harvesting operations to follow the contours of the field. While each of these prior art systems may serve their intended purpose and while each may perform adequately under most circumstances, heretofore, there have been no header height control systems that can provide the necessary sensitivity and responsiveness needed for corn headers when the crop divider snouts are being run at or near the ground in an effort to pick up “downed” corn, i.e., when the corn stalks are lying on the ground due to wind storms or other circumstances.
U.S. Pat. No. 6,202,395 to Gramm (hereinafter “Gramm '395”) and U.S. Pat. No. 6,523,333 to Metzger (hereinafter Metzger '333), both of which are hereby incorporated herein in their entirety by reference, describe the need for automatically controlling header height and the advantages achieved through the use of height sensors mounted near the snout tips of the header. In both Gramm '395 and Metzger '333 the height sensors generate output signals of varying magnitude based on the rotational position of the sensing arm relative to the crop divider snout. The electrical output signals from the height sensors are communicated to the combine's header control system to automatically actuate the combine's hydraulics to raise and lower the header in response to the output signals of the height sensor. Neither Gramm '395 nor Metzger '333, however, discuss the effects of the sensitivity or responsiveness of the height sensor when the crop divider snouts are being run at or near the ground.
Although it is advantageous to place height sensors near the tips of the snouts for the reasons disclosed in Gramm '395 and Metzger '333, it should be appreciated that after the snout tips touch the ground and the rest of header continues to be lowered, the actual header height will no longer have the same near-linear proportionality to the movement of the height sensing arms because the height sensor arm will rotate very little relative to the snout to which it is mounted. As a result, a larger effective “dead band” is developed at the most critical operating heights of the header, thereby increasing likelihood of impact of the header with the ground surface or the undesired loss of crop should the operator choose instead to raise the header to avoid the chance of ground impact. Even with the proportional header control systems available on late model combines which cause the headers to raise quicker when the height sensors indicate abrupt ground elevation changes, the responsiveness of such proportional systems is still compromised when the snouts are being run at ground level due to the limited rotational movement of the height sensor at such positions.
Accordingly, there is a need for a header height control system that takes advantage of a height sensor located as far forward on the crop dividing snout as practicable to allow earlier ground sensing so as to provide maximum warning time for the header height control system to respond to terrain changes, while at the same time improving the responsiveness of the control system when the header is being run at or near the ground surface.